The present invention relates to methods of permanently attaching a fastening element, such as a nut or bolt, to a metal panel. The method of this invention is particularly useful for mass production applications, such as used by the automotive and appliance industries where a secure fastener installation is required in metal panels having a range of panel thicknesses. More specifically, the present invention relates to an improved riveting technique for flush mounting of a fastening element in panels having a range of panel thicknesses.
Pierce nuts, such as disclosed in U.S. Pat. No. 2,707,322, have been widely accepted in mass production applications such as the automotive industry. More recent improvements in pierce nuts, such as shown in U.S. Pat. No. 3,648,747, have resulted in improved retention of the pierce nut in the panel, although the original universal pierce nut remains a preferred installation in many applications. In both types of pierce nuts, several nuts may be installed in a metal plate or panel wherein the plate or panel may be simultaneously formed into a contoured shape, such as an automotive body panel or structural support.
More recently, fastening systems have been developed to permanently install both male and female fasteners in a panel in mass production applications, such as shown in U.S. Pat. Nos. 4,555,838 and 4,610,072. The fastening element in such fastening systems include a tubular or annular barrel portion which is riveted to the panel during the installation. The tubular barrel portion may be utilized to pierce a slug from the panel, which may be received in the tubular barrel portion, as disclosed in U.S. Pat. No. 4,555,838, or a punch may be utilized to pre-pierce the panel as disclosed, for example, in U.S. Pat. Nos. 4,711,021, 4,831,698 and 4,713,872. Although such fasteners have achieved commercial success, the use of such fasteners in mass production applications has been somewhat limited by the range of panel thicknesses utilized by the automotive industry, for example, and in certain applications requiring improved torque resistance in thin panels.
The need remains for a universal fastening system utilizing conventional installation tooling which may be used for a wide-range of panel thicknesses and preferably having improved torque resistance. The improved fastener and panel assembly must also have good push out and pull through strength and be adapted for mass production applications.